Financial Instruments and Fair Value Measurements - Summary of Undesignated Financial Instruments Exercised and Realized and Unrealized Gains (Losses) in Foreign Currency and Derivative Gains (Losses) Net (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) Contract	Mar. 31, 2018 USD ($) Contract
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Exercised contracts | Contract	23	15
Realized gains (losses) on the matured, expired or settled contracts	$ 1	$ (7)
Unrealized gains (losses) on the change in fair value of outstanding contracts	$ 7	$ (13)